LockCrypt Ransomware Distributed Using Brute Force RDP Attacks

A malware threat called LockCrypt ransomware is being used in widespread attacks on businesses in the United States, United Kingdom, and South Africa. While ransomware is commonly spread via spam email, this campaign spreads the file-encrypting malware via remote desktop protocol brute force attacks.

The LockCrypt ransomware attacks were first detected in June this year, but over the past few months the number of attacks has increased significantly, with October seeing the highest number of attacks so far this year.

LockCrypt ransomware is a relatively new malware variant, having first been seen in June 2017. Once infected, users will be unable to access their files. This ransomware variant uses RSA-2048 and AES-256 cryptopgraphy, which makes it virtually impossible to recover files without paying the ransom demand if a viable backup does not exist. To make recovery more difficult, LockCrypt ransomware also deletes Windows Shadow Volume copies. Encrypted files are given the .lock extension.

The ransom payment for this campaign is considerable – typically between 0.5 and 1 Bitcoin per encrypted server. That’s between $3,963 and $7,925 per compromised server; however, since the same login credentials are often used for RDP access on multiple servers, once one password is correctly guessed, it can be used to access multiple servers and deploy LockCrypt ransomware. One of the Bitcoin addresses used by the attackers shows one company paid a ransom of $19,000 to recover files on three of its servers.

Once access to a server is gained, ransomware is deployed; however, the attackers are manually interacting with compromised servers. AlientVault security researcher, Chris Doman, reported that for one company, in addition to deploying ransomware, the attackers “manually killed business critical processes for maximum damage.” All non-core processes on an infected server are killed.

The attacks do not appear to be targeted, instead they are randomly conducted on business servers. Businesses that are most likely to have ransomware installed are those that have failed to use complex passwords for RDP access. While it may be tempting to set an easy-to-remember password, this plays into the hands of attackers.

Other security controls such as two-factor authentication can reduce the risk from this type of attack, as can rate limiting to prevent the number of failed attempts a user can make before their IP address is temporarily – or permanently – blocked.

An additional control that system administrators can apply is to white-list certain IP addresses to restrict RDP access to authorized individuals. If that is not practical, disallowing RDP connections over the Internet from abroad can help to prevent these attacks.

While implementing controls to prevent RDP brute force attacks is vital, most ransomware variants are spread via spam email, and to a lesser extent via exploit kits and drive-by downloads. Comprehensive security defenses must therefore be deployed to reduce the risk of ransomware attacks.